Parents' smoking damages their kids' lungs.

A woman's smoking during pregnancy can detrimentally affect her child's lung function into adulthood, conclude three groups of investigators from the Harvard School of Public Health. And those effects, it seems, are irreversible.

Many of the investigators are involved in the Harvard Six Cities Study, which has been building a body of knowledge about air pollution and lung hazards for 20 years. Separate reports in the June 1 and June 15 AMERICAN JOURNAL OF EPIDEMIOLOGY (AJE) and in the June AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE (AJRCCM) provide strong evidence that both maternal and paternal smoking create long-term -- perhaps even lifetime -- health dangers for children.

In all of the studies, children were asked to blow into the tube of a spirometer, which measures the volume of air that can be moved in and out of the lungs. Overall, the offspring of smokers blew less air.

The AJRCCM study examined 8,700 children age 6 to 18 in six cities in the United States and found that those exposed to tobacco smoke before the age of 6 had a 2 to 3 percent decrease in lung function, or capacity. Twelve years later, those children still exhibited reduced lung function.

Normally, human lung function begins to decrease in the late 20s or early 30s, says Lucas Neas, coauthor of the June 1 AJE study. Decreased breathing capacity caused by lost lung function can be counteracted by vigorous exercise, he adds, though lost lung function can never be regained. In addition, the study finds that children who grow up in smoking households stand a greater chance of developing a host of lower respiratory symptoms, including shortness of breath, persistent wheeze, chronic cough and phlegm, and bronchitis.

"As vital [lung] capacity declines, your capacity for life itself declines," Neas explains.

The June 1 AJE study of 2,994 white children between the ages of 7 and 11 in six U.S. cities from 1983 through 1988 corroborated the link between parental smoking and respiratory harm to children. But unlike other studies, this one integrates the effects of indoor air pollution caused by passive smoke and ambient air pollution, comments C. Arden Pope III of Brigham Young University in Provo, Utah.

"These studies were designed to look at both indoor and outdoor exposures," says Pope, "and are clearly superior to other studies." However, he adds, "The jury's still out on whether or not it's prenatal or postnatal exposure that causes harm."

The June 15 AJE study looked at 8,863 white children age 8 to 12 in 22 North American communities and finds a weak correlation between prenatal smoking and first-trimester harm to the fetal lungs. Researchers know that smoking moms give birth to smaller babies, but little is known about the connection between low birthweight and reduced lung function. Some suspect that the lungs of fetuses whose mothers smoke, like those of fetal rats in laboratory tests, weigh less and produce less elastin (the main protein of the lung's elastic tissue fibers), thus decreasing pulmonary function.

Maternal smoking has also been linked to hearing defects in children (SN: 7/10/93, p.23). Moreover, the May PEDIATRICS raised the question of a link between smoking mothers and sleep apneas, which are thought to contribute to sudden infant death syndrome (SIDS).

Morton Lippmann of New York University's Institute of Environmental Medicine in Tuxedo, N.Y., says the evidence linking prenatal smoking and SIDS is inconclusive at this time. However, he is quick to say that the AJE studies represent "the latest, most complete, and most definitive research [on parental smoking] so far. I admire the quality and persistence of the work."